All current protein purification systems show deficiencies, especially for large-scale purifications. In particular, the purification of antibodies is inadequate as far as purity and yields are concerned. Consequently, the present state of the art processes are costly due to large volumes of solvents and long production times for making pure immunoglobulins intended for therapeutic and diagnostic applications.
In an affinity separation, the protein being purified adsorbs selectively and reversibly to a complimentary binding substance or affinity ligand, often times an antibody molecule. Affinity separation generally results in very low non-specific binding compared to other separation techniques. The very low non-specific binding makes it possible to purify a given protein from complex biological mixtures, to separate incorrectly folded forms from native molecules, and to recover the protein.
Purification systems using glass or metal tubes that contain a packed column of separation medium, for example, beads or particles, are known. These tubes are known as column boxes. Because the separation medium is compacted within the column boxes, the flow rates are slow and the column boxes have a limited capacity. Therefore, prior art purification technology has focused on increasing the porosity of the separation medium to increase the flow rates and capacity within the column box. The object of these known systems is to purify the largest amount of material within the shortest amount of time while keeping the amount of contaminants in the product low and the product yields high. One problem with the old purification technology is that increasing porosity of the separation medium achieved faster flow rates and capacity, but reduced product yields and purity.
Orbicell™ cellulose beads are available from Accurate Polymers, Ltd. in Illinois and described in U.S. Pat. No. 6,315,900 issued on Nov. 1, 2001 to Stipanovic et al. entitled Static Separation Method Using Non-Porous Cellulose Beads, incorporated herein by reference.
A typical affinity adsorbent consists of a solid support, a spacer arm, and a ligand. The spacer arm may encourage protein binding by making the ligand more accessible. Certain affinity separation products do not have a spacer arm of sufficient length or suitable nature so as to aid in the attachment of the target compound, for example, an antibody. In order to overcome this limitation, there is a need for a spacer arm that would allow for better orientation of the ligand, decreased steric hindrance between the target compounds, and decreased steric hindrance between the ligands thereby allowing for greater attachment of the target compound. Ease in attachment of the target compound to the ligand due to the geometry of the spacer arm and/or ligand increases target compound yield. There is a need in the art for the ligand to exhibit specific and reversible binding to the target compound, for example, a protein such as an antibody.
Affinity chromatography on immobilized Staphylococcus Aureus Protein A (SpA), Protein G and Protein M columns is a recent purification method for monoclonal and polyclonal antibody production. These bacteria-derived proteins are not only costly to produce, but also suffer from biological and chemical instability. An ability to be cleaned and sterilized is an absolute requirement by regulatory authorities for sorbents used to purify antibodies destined for therapeutic end use. Polyclonal antibodies, as well as more recently developed monoclonals, are routinely purified by affinity column chromatography. These antibodies have wide applications in the diagnostic field, but lately similar antibodies are more and more finding their use in therapeutic applications. The latter application can hardly tolerate any instability of affinity sorbents, which becomes especially critical when steam, or harsh chemical sterilization procedures are mandated by regulatory agencies.
Of course, the therapeutic end-use will create a demand for much larger quantities of highly purified antibodies than the diagnostic field ever did. The first obstacle that the present state of the art-technology faces on any future scale-ups is the high cost of these bacteria-derived proteins. On top of the high cost of sorbents will be the regulatory authorities thorough scrutiny of potential instabilities of sorbents during the required sterilization protocols. Therefore, there is a need in the art to solve these and other difficulties of the prior art.
Recent advances in molecular modeling have enabled research groups to come up with much smaller molecules than bacteria-derived proteins, which surprisingly, can still simulate high affinity and selectivity of respective bacterial proteins for numerous immunoglobulins. Said model synthetic compounds possessing affinity for antibodies range from simple monocyclic and polycyclic compounds to peptides of short to medium length. Some of these peptides are linear while others have macrocyclic structure.